Use the Feynman technique to expose gaps in your knowledge

The Feynman Technique involves the learner writing an in-depth explanation of the area they are trying to learn.

One of the reasons this is useful is that as the learner starts to delve into more depth, it calls into contrast the areas where understanding doesn't exist in a specific and targeted way. The areas you don't understand become more obvious.

This lets you direct future energy into filling these gaps, either through direct research or through understanding better questions to ask someone who does understand.